xamarin android 文件选择

调出选择界面：

            Intent intent = new Intent(Intent.ActionGetContent);
            intent.AddCategory(Intent.CategoryOpenable);
            intent.SetType("file/*");
            StartActivityForResult(Intent.CreateChooser(intent, "选择备份文件"), 20);

接收选择结果：

protected override void OnActivityResult(int requestCode, [GeneratedEnum] Result resultCode, Intent data)
        {
            if (requestCode == 20)
            {
                var uri = data.Data as Android.Net.Uri;
                var filepath = uri.Path;
            }
            base.OnActivityResult(requestCode, resultCode, data);
        }